Audio signal processing apparatus

ABSTRACT

In an audio signal encoding apparatus, a first audio signal and a second audio signal are added into an addition-result signal. The first audio signal is subtracted from the second audio signal to generate a subtraction-result signal. A first difference signal is generated which represents a difference in the addition-result signal. A second difference signal is generated which represents a difference in the subtraction-result signal. A plurality of first predictors have different prediction characteristics respectively, and are responsive to the first difference signal for generating first different prediction signals for the first difference signal, respectively. A plurality of first subtracters operate for generating first prediction-error signals representing differences between the first difference signal and the first different prediction signals, respectively. A first minimum prediction-error signal representative of a smallest difference is selected from among the first prediction-error signals. A plurality of second predictors have different prediction characteristics respectively, and are responsive to the second difference signal for generating second different prediction signals for the second difference signal, respectively. A plurality of second subtracters operate for generating second prediction-error signals representing differences between the second difference signal and the second different prediction signals, respectively. A second minimum prediction-error signal representative of a smallest difference is selected from among the second prediction-error signals.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to an audio signal encoding apparatus.This invention also relates to an optical recording medium. In addition,this invention relates to an audio signal decoding apparatus.Furthermore, this invention relates to a method of transmitting an audiosignal.

[0003] 2. Description of the Related Art

[0004] Highly efficient encoding of an audio signal includes a step ofcompressing the audio signal. Highly efficient encoding techniques areclassified into two types; the lossy encoding techniques and thelossless encoding techniques. Among the lossy encoding techniques, the“acoustic encoding” is well known as a technique which renders the datadeterioration acoustically undetectable. On the other hand, according tothe lossless encoding and decoding techniques, the recovered data areexactly the same as the original data.

[0005] In general, a sampled or uniformly quantized audio signal hassignificant redundancy. During the encoding of such an audio signal, thedegree of the compression of the audio signal rises as redundancy ismore effectively removed therefrom.

SUMMARY OF THE INVENTION

[0006] It is a first object of this invention to provide an audio signalencoding apparatus having a higher compression performance.

[0007] It is a second object of this invention to provide an improvedoptical recording medium.

[0008] It is a third object of this invention to provide an improvedaudio signal decoding apparatus.

[0009] It is a fourth object of this invention to provide an improvedmethod of transmitting an audio signal.

[0010] A first aspect of this invention provides an audio signalencoding apparatus comprising means for adding a first audio signal anda second audio signal into an addition-result signal; means forsubtracting the first audio signal from the second audio signal, andgenerating a subtraction-result signal; means responsive to theaddition-result signal for generating a first difference signalrepresenting a difference in the addition-result signal; meansresponsive to the subtraction-result signal for generating a seconddifference signal representing a difference in the subtraction-resultsignal; a plurality of first predictors having different predictioncharacteristics respectively and being responsive to the firstdifference signal for generating first different prediction signals forthe first difference signal, respectively; a plurality of firstsubtracters for generating first prediction-error signals representingdifferences between the first difference signal and the first differentprediction signals, respectively; means for selecting a first minimumprediction-error signal representative of a smallest difference fromamong the first prediction-error signals; a plurality of secondpredictors having different prediction characteristics respectively andbeing responsive to the second difference signal for generating seconddifferent prediction signals for the second difference signal,respectively; a plurality of second subtracters for generating secondprediction-error signals representing differences between the seconddifference signal and the second different prediction signals,respectively; and means for selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals.

[0011] A second aspect of this invention is based on the first aspectthereof, and provides an audio signal encoding apparatus furthercomprising means for generating a variable-rate bit stream in responseto the first minimum prediction-error signal and the second minimumprediction-error signal.

[0012] A third aspect of this invention provides an audio signaldecoding apparatus for processing a first minimum prediction-errorsignal and a second minimum prediction-error signal which are generatedby an audio signal encoding apparatus comprising means for adding afirst audio signal and a second audio signal into an addition-resultsignal; means for subtracting the first audio signal from the secondaudio signal, and generating a subtraction-result signal; meansresponsive to the addition-result signal for generating a firstdifference signal representing a difference in the addition-resultsignal; means responsive to the subtraction-result signal for generatinga second difference signal representing a difference in thesubtraction-result signal; a plurality of first predictors havingdifferent prediction characteristics respectively and being responsiveto the first difference signal for generating first different predictionsignals for the first difference signal, respectively; a plurality offirst subtracters for generating first prediction-error signalsrepresenting differences between the first difference signal and thefirst different prediction signals, respectively; means for selecting afirst minimum prediction-error signal representative of a smallestdifference from among the first prediction-error signals; a plurality ofsecond predictors having different prediction characteristicsrespectively and being responsive to the second difference signal forgenerating second different prediction signals for the second differencesignal, respectively; a plurality of second subtracters for generatingsecond prediction-error signals representing differences between thesecond difference signal and the second different prediction signals,respectively; and means for selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals. The audio signal decoding apparatus comprisesmeans for recovering the addition-result signal from the first minimumprediction-error signal; means for recovering the subtraction-resultsignal from the second minimum prediction-error signal; and means forrecovering the first audio signal and the second audio signal from therecovered addition-result signal and the recovered subtraction-resultsignal.

[0013] A fourth aspect of this invention provides a method comprisingthe steps of adding a first audio signal and a second audio signal intoan addition-result signal; subtracting the first audio signal from thesecond audio signal, and generating a subtraction-result signal;generating a first difference signal representing a difference in theaddition-result signal; generating a second difference signalrepresenting a difference in the subtraction-result signal; generatingfirst different prediction signals for the first difference signal,respectively; generating first prediction-error signals representingdifferences between the first difference signal and the first differentprediction signals, respectively; selecting a first minimumprediction-error signal representative of a smallest difference fromamong the first prediction-error signals; generating second differentprediction signals for the second difference signal, respectively;generating second prediction-error signals representing differencesbetween the second difference signal and the second different predictionsignals, respectively; selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals; and transmitting the first minimumprediction-error signal and the second minimum prediction-error signalto a communication line.

[0014] A fifth aspect of this invention provides an optical recordingmedium storing formatted information of a first minimum prediction-errorsignal and a second minimum prediction-error signal which are generatedby an audio signal encoding apparatus comprising means for adding afirst audio signal and a second audio signal into an addition-resultsignal; means for subtracting the first audio signal from the secondaudio signal, and generating a subtraction-result signal; meansresponsive to the addition-result signal for generating a firstdifference signal representing a difference in the addition-resultsignal; means responsive to the subtraction-result signal for generatinga second difference signal representing a difference in thesubtraction-result signal; a plurality of first predictors havingdifferent prediction characteristics respectively and being responsiveto the first difference signal for generating first different predictionsignals for the first difference signal, respectively; a plurality offirst subtracters for generating first prediction-error signalsrepresenting differences between the first difference signal and thefirst different prediction signals, respectively; means for selecting afirst minimum prediction-error signal representative of a smallestdifference from among the first prediction-error signals; a plurality ofsecond predictors having different prediction characteristicsrespectively and being responsive to the second difference signal forgenerating second different prediction signals for the second differencesignal, respectively; a plurality of second subtracters for generatingsecond prediction-error signals representing differences between thesecond difference signal and the second different prediction signals,respectively; and means for selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals.

[0015] A sixth aspect of this invention provides a method ofnetwork-based transmission which comprises the steps of adding a firstaudio signal and a second audio signal into an addition-result signal;subtracting the first audio signal from the second audio signal, andgenerating a subtraction-result signal; generating a first differencesignal representing a difference in the addition-result signal;generating a second difference signal representing a difference in thesubtraction-result signal; generating first different prediction signalsfor the first difference signal, respectively; generating firstprediction-error signals representing differences between the firstdifference signal and the first different prediction signals,respectively; selecting a first minimum prediction-error signalrepresentative of a smallest difference from among the firstprediction-error signals; generating second different prediction signalsfor the second difference signal, respectively; generating secondprediction-error signals representing differences between the seconddifference signal and the second different prediction signals,respectively; selecting a second minimum prediction-error signalrepresentative of a smallest difference from among the secondprediction-error signals; and transmitting the first minimumprediction-error signal and the second minimum prediction-error signalto a communication line.

[0016] A seventh aspect of this invention provides an audio signalencoding apparatus comprising means for selecting a first audio signaland a second audio signal from among signals composing a multi-channelaudio signal; means for adding the first audio signal and the secondaudio signal into an addition-result signal; means for subtracting thefirst audio signal from the second audio signal, and generating asubtraction-result signal; means responsive to the addition-resultsignal for generating a first difference signal representing adifference in the addition-result signal; means responsive to thesubtraction-result signal for generating a second difference signalrepresenting a difference in the subtraction-result signal; a pluralityof first predictors having different prediction characteristicsrespectively and being responsive to the first difference signal forgenerating first different prediction signals for the first differencesignal, respectively; a plurality of first subtracters for generatingfirst prediction-error signals representing differences between thefirst difference signal and the first different prediction signals,respectively; means for selecting a first minimum prediction-errorsignal representative of a smallest difference from among the firstprediction-error signals; a plurality of second predictors havingdifferent prediction characteristics respectively and being responsiveto the second difference signal for generating second differentprediction signals for the second difference signal, respectively; aplurality of second subtracters for generating second prediction-errorsignals representing differences between the second difference signaland the second different prediction signals, respectively; and means forselecting a second minimum prediction-error signal representative of asmallest difference from among the second prediction-error signals.

[0017] An eighth aspect of this invention is based on the seventh aspectthereof, and provides an audio signal encoding apparatus furthercomprising means for generating a variable-rate bit stream in responseto the first minimum prediction-error signal and the second minimumprediction-error signal.

[0018] A ninth aspect of this invention provides an audio signaldecoding apparatus for processing a first minimum prediction-errorsignal and a second minimum prediction-error signal which are generatedby an audio signal encoding apparatus comprising means for selecting afirst audio signal and a second audio signal from among signalscomposing a multi-channel audio signal; means for adding the first audiosignal and the second audio signal into an addition-result signal; meansfor subtracting the first audio signal from the second audio signal, andgenerating a subtraction-result signal; means responsive to theaddition-result signal for generating a first difference signalrepresenting a difference in the addition-result signal; meansresponsive to the subtraction-result signal for generating a seconddifference signal representing a difference in the subtraction-resultsignal; a plurality of first predictors having different predictioncharacteristics respectively and being responsive to the firstdifference signal for generating first different prediction signals forthe first difference signal, respectively; a plurality of firstsubtracters for generating first prediction-error signals representingdifferences between the first difference signal and the first differentprediction signals, respectively; means for selecting a first minimumprediction-error signal representative of a smallest difference fromamong the first prediction-error signals; a plurality of secondpredictors having different prediction characteristics respectively andbeing responsive to the second difference signal for generating seconddifferent prediction signals for the second difference signal,respectively; a plurality of second subtracters for generating secondprediction-error signals representing differences between the seconddifference signal and the second different prediction signals,respectively; and means for selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals. The audio signal decoding apparatus comprisesmeans for recovering the addition-result signal from the first minimumprediction-error signal; means for recovering the subtraction-resultsignal from the second minimum prediction-error signal; and means forrecovering the first audio signal and the second audio signal from therecovered addition-result signal and the recovered subtraction-resultsignal.

[0019] A tenth aspect of this invention provides a method comprising thesteps of selecting a first audio signal and a second audio signal fromamong signals composing a multi-channel audio signal; adding the firstaudio signal and the second audio signal into an addition-result signal;subtracting the first audio signal from the second audio signal, andgenerating a subtraction-result signal; generating a first differencesignal representing a difference in the addition-result signal;generating a second difference signal representing a difference in thesubtraction-result signal; generating first different prediction signalsfor the first difference signal, respectively; generating firstprediction-error signals representing differences between the firstdifference signal and the first different prediction signals,respectively; selecting a first minimum prediction-error signalrepresentative of a smallest difference from among the firstprediction-error signals; generating second different prediction signalsfor the second difference signal, respectively; generating secondprediction-error signals representing differences between the seconddifference signal and the second different prediction signals,respectively; selecting a second minimum prediction-error signalrepresentative of a smallest difference from among the secondprediction-error signals; and transmitting the first minimumprediction-error signal and the second minimum prediction-error signalto a communication line.

[0020] An eleventh aspect of this invention provides an opticalrecording medium storing formatted information of a first minimumprediction-error signal and a second minimum prediction-error signalwhich are generated by an audio signal encoding apparatus comprisingmeans for selecting a first audio signal and a second audio signal fromamong signals composing a multi-channel audio signal; means for addingthe first audio signal and the second audio signal into anaddition-result signal; means for subtracting the first audio signalfrom the second audio signal, and generating a subtraction-resultsignal; means responsive to the addition-result signal for generating afirst difference signal representing a difference in the addition-resultsignal; means responsive to the subtraction-result signal for generatinga second difference signal representing a difference in thesubtraction-result signal; a plurality of first predictors havingdifferent prediction characteristics respectively and being responsiveto the first difference signal for generating first different predictionsignals for the first difference signal, respectively; a plurality offirst subtracters for generating first prediction-error signalsrepresenting differences between the first difference signal and thefirst different prediction signals, respectively; means for selecting afirst minimum prediction-error signal representative of a smallestdifference from among the first prediction-error signals; a plurality ofsecond predictors having different prediction characteristicsrespectively and being responsive to the second difference signal forgenerating second different prediction signals for the second differencesignal, respectively; a plurality of second subtracters for generatingsecond prediction-error signals representing differences between thesecond difference signal and the second different prediction signals,respectively; and means for selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals.

[0021] A twelfth aspect of this invention provides a method ofnetwork-based transmission which comprises the steps of selecting afirst audio signal and a second audio signal from among signalscomposing a multi-channel audio signal; adding the first audio signaland the second audio signal into an addition-result signal; subtractingthe first audio signal from the second audio signal, and generating asubtraction-result signal; generating a first difference signalrepresenting a difference in the addition-result signal; generating asecond difference signal representing a difference in thesubtraction-result signal; generating first different prediction signalsfor the first difference signal, respectively; generating firstprediction-error signals representing differences between the firstdifference signal and the first different prediction signals,respectively; selecting a first minimum prediction-error signalrepresentative of a smallest difference from among the firstprediction-error signals; generating second different prediction signalsfor the second difference signal, respectively; generating secondprediction-error signals representing differences between the seconddifference signal and the second different prediction signals,respectively; selecting a second minimum prediction-error signalrepresentative of a smallest difference from among the secondprediction-error signals; and transmitting the first minimumprediction-error signal and the second minimum prediction-error signalto a communication line.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a block diagram of a system including an audio signalencoding apparatus and an audio signal decoding apparatus according to afirst embodiment of this invention.

[0023]FIG. 2 is a block diagram of a lossless encoder in FIG. 1.

[0024]FIG. 3 is a diagram of the format of a 1-frame-correspondingsegment of a variable-rate bit stream generated by the audio signalencoding apparatus in FIG. 1.

[0025]FIG. 4 is a block diagram of a lossless decoder in FIG. 1.

[0026]FIG. 5 is a block diagram of a lossless encoder in a secondembodiment of this invention.

[0027]FIG. 6 is a block diagram of a lossless decoder in the secondembodiment of this invention.

[0028]FIG. 7 is a block diagram of an audio signal encoding apparatus ina third embodiment of this invention.

[0029]FIG. 8 is a block diagram of an audio signal decoding apparatus inthe third embodiment of this invention.

[0030]FIG. 9 is a block diagram of a system according to a fourthembodiment of this invention.

[0031]FIG. 10 is a diagram of the structure of an audio pack.

[0032]FIG. 11 is a diagram of the structure of the audio pack.

[0033]FIG. 12 is a block diagram of a system according to a fifthembodiment of this invention.

[0034]FIG. 13 is a flowchart of a segment of a control program for apacketing processor in FIG. 12.

[0035]FIG. 14 is a flowchart of a segment of a control program for ade-packeting processor in FIG. 12.

[0036]FIG. 15 is a block diagram of a system including an audio signalencoding apparatus and an audio signal decoding apparatus according to asixth embodiment of this invention.

[0037]FIG. 16 is a diagram of the format of a 1-frame-correspondingsegment of a variable-rate bit stream generated in the system of FIG.15.

[0038]FIG. 17 is a block diagram of a system including an audio signalencoding apparatus and an audio signal decoding apparatus according to aseventh embodiment of this invention.

[0039]FIG. 18 is a diagram of the format of a 1-frame-correspondingsegment of a variable-rate bit stream generated in the system of FIG.17.

[0040]FIG. 19 is a block diagram of a system including an audio signalencoding apparatus and an audio signal decoding apparatus according toan eighth embodiment of this invention.

[0041]FIG. 20 is a block diagram of a system including an audio signalencoding apparatus and an audio signal decoding apparatus according to aninth embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

[0042] With reference to FIG. 1, an audio signal encoding apparatus 100includes a channel correlation circuit “A” and a lossless encoder 2D. Anaudio signal decoding apparatus 200 includes a channel correlationcircuit “B” and a lossless decoder 3D. The audio signal encodingapparatus 100 and the audio signal decoding apparatus 200 are connectedvia a transmission line 250.

[0043] The audio signal encoding apparatus 100 receives stereophonic2-channel digital audio signals, that is, a left-channel digital audiosignal “L” and a right-channel digital audio signal “R”. Thestereophonic 2-channel digital audio signals are reproduced from adigital recording medium such as a DVD-audio (a digital versatile discaudio). The audio signal encoding apparatus 100 encodes the left-channeldigital audio signal “L” and the right-channel digital audio signal “R”into encoding-resultant digital audio signals. The audio signal encodingapparatus 100 outputs the encoding-resultant digital audio signals tothe transmission line 250. The encoding-resultant digital audio signalsare propagated to the audio signal decoding apparatus 200 via thetransmission line 250. The audio signal decoding apparatus 200 decodesthe encoding-resultant digital audio signals into the originalleft-channel digital audio signal “L” and the original right-channeldigital audio signal “R”. In other words, the audio signal decodingapparatus 200 recovers the original left-channel digital audio signal“L” and the original right-channel digital audio signal “R”. The audiosignal decoding apparatus 200 outputs the recovered left-channel digitalaudio signal “L” and the recovered right-channel digital audio signal“R” to an external apparatus.

[0044] The channel correlation circuit “A” in the audio signal encodingapparatus 100 includes an addition circuit 1 a and a subtraction circuit1 b. The addition circuit 1 a receives the left-channel digital audiosignal “L” and the right-channel digital audio signal “R”. Theleft-channel digital audio signal “L” results from quantization of aleft-channel analog audio signal at a predetermined sampling frequencyand a predetermined quantization bit number. The predetermined samplingfrequency is equal to, for example, 192 kHz. The predeterminedquantization bit number is equal to, for example, 24. Similarly, theright-channel digital audio signal “R” results from quantization of aright-channel analog audio signal at the predetermined samplingfrequency and the predetermined quantization bit number. The additioncircuit la adds the left-channel digital audio signal “L” and theright-channel digital audio signal “R” into an addition-result signal(L+R). The addition-result signal (L+R) is a PCM (pulse code modulation)signal. The addition circuit la outputs the addition-result signal (L+R)to the lossless encoder 2D. The subtraction circuit 1 b receives theleft-channel digital audio signal “L” and the right-channel digitalaudio signal “R”. The subtraction circuit 1 b subtracts theright-channel digital audio signal “R” from the left-channel digitalaudio signal “L”, thereby generating a subtraction-result signal (L−R).The subtraction-result signal (L−R) is a PCM signal. The subtractioncircuit 1 b outputs the subtraction-result signal (L−R) to the losslessencoder 2D.

[0045] As shown in FIG. 2, the lossless encoder 2D includes a buffer (amemory) 10. A sequence of samples of the addition-result signal (L+R)and a sequence of samples of the subtraction-result signal (L−R) areapplied to the buffer 10. The addition-result signal (L+R) and thesubtraction-result signal (L−R) are stored into the buffer 10 frame byframe. Every frame is composed of a predetermined number of successivesamples.

[0046] Samples of the addition-result signal (L+R) are sequentiallytransmitted from the buffer 10 to a difference calculation circuit 11D1.The difference calculation circuit 11D1 generates a signal Δ(L+R)representing the difference between the current sample of theaddition-result signal (L+R) and the immediately preceding samplethereof. The difference calculation circuit 11D1 outputs the differencesignal Δ(L+R) to a prediction circuit 15D1 sample by sample. In otherwords, the differential calculation circuit 11D1 implements differentialpulse code modulation (DPCM) of the addition-result signal (L+R), andoutputs the resultant DPCM signal Δ(L+R).

[0047] Samples of the subtraction-result signal (L−R) are sequentiallytransmitted from the buffer 10 to a difference calculation circuit 11D2.The difference calculation circuit 11D2 generates a signal Δ(L−R)representing the difference between the current sample of thesubtraction-result signal (L−R) and the immediately preceding samplethereof. The difference calculation circuit 11D2 outputs the differencesignal Δ(L−R) to a prediction circuit 15D2 sample by sample. In otherwords, the differential calculation circuit 11D2 implements differentialpulse code modulation (DPCM) of the subtraction-result signal (L−R), andoutputs the resultant DPCM signal Δ(L−R).

[0048] For every frame, the first sample of the addition-result signal(L+R) and the first sample of the subtraction-result signal (L−R) aretransmitted from the buffer 10 to a multiplexer 19.

[0049] The prediction circuit 15D1 includes predictors 12 a-1, 12 a-2, .. . , and 12 a-n, and subtracters 13 a-1, 13 a-2, . . . , and 13 a-n,where “n” denotes a predetermined natural number equal to or greaterthan 2. The predictors 12 a-1, 12 a-2, . . . , and 12 a-n receive everysample of the difference signal Δ(L+R) from the difference calculationcircuit 11D1. Also, the subtracters 13 a-1, 13 a-2, . . . , and 13 a-nreceive every sample of the difference signal Δ(L+R) from the differencecalculation circuit 11D1. The predictors 12 a-1, 12 a-2, . . . , and 12a-n have different prediction characteristics, respectively.Specifically, the predictors 12 a-1, 12 a-2, . . . , and 12 a-n aredifferent from each other in prediction coefficients. Each of thepredictors 12 a-1, 12 a-2, . . . , and 12 a-n predicts a current sampleof the difference signal Δ(L+R) from preceding samples thereof inresponse to the related prediction coefficients. Thus, the predictors 12a-1, 12 a-2, . . . , and 12 a-n generate prediction-result signals forthe difference signal Δ(L+R) in response to the prediction coefficients,respectively. The predictors 12 a-1, 12 a-2, . . . , and 12 a-n outputthe prediction-result signals to the subtracters 13 a-1, 13 a-2, . . . ,and 13 a-n respectively. For every sample, each of the subtracters 13a-1, 13 a-2, . . . , and 13 a-n subtracts the related prediction-resultsignal from the difference signal Δ(L+R), and hence generates a signalrepresenting the prediction error between the prediction-result signaland the difference signal Δ(L+R). The subtracters 13 a-1, 13 a-2, . . ., and 13 a-n output the respective prediction-error signals to a bufferand selector 16D1.

[0050] The prediction-error signals, that is, the output signals of thesubtracters 13 a-1, 13 a-2, . . . , and 13 a-n, are temporarily storedin a memory within the buffer and selector 16D1. A selection signalgenerator 17 produces a first selection signal. The selection signalgenerator 17 outputs the first selection signal to the buffer andselector 16D1. The first selection signal is designed to select thesmallest one from among the prediction-error signals in the memory ofthe buffer and selector 16D1 as an output signal of an optimumsubtracter (an optimum predictor) for every sub-frame. Specifically, forevery sub-frame, the selection signal generator 17 searches the memorywithin the buffer and selector 16D1 for the smallest prediction-errorsignal. In more detail, for every sub-frame, the sums of the valuesrepresented by samples of the respective prediction-error signals arecalculated. The calculated sums are compared to determine the smallestone which corresponds to the smallest prediction-error signal to beselected. The selection signal generator 17 enables the buffer andselector 16D1 to output the smallest prediction-error signal from thememory to a packing circuit 18 as the selected (L+R)-relatedprediction-error signal for every sub-frame.

[0051] Every sub-frame is composed of a predetermined number ofsuccessive samples. Several tens of successive sub-frames compose oneframe. For example, 80 successive sub-frames compose one frame.

[0052] The prediction circuit 15D2 includes predictors 12 b-1, 12 b-2, .. . , and 12 b-n, and subtracters 13 b-1, 13 b-2, . . . , and 13 b-n.The predictors 12 b-1, 12 b-2, . . . , and 12 b-n receive every sampleof the difference signal Δ(L−R) from the difference calculation circuit11D2. Also, the subtracters 13 b-1, 13 b-2, . . . , and 13 b-n receiveevery sample of the difference signal Δ(L−R) from the differencecalculation circuit 11D2. The predictors 12 b-1, 12 b-2, . . . , and 12b-n have different prediction characteristics, respectively.Specifically, the predictors 12 b-1, 12 b-2, . . . , and 12 b-n aredifferent from each other in prediction coefficients. Each of thepredictors 12 b-1, 12 b-2, . . . , and 12 b-n predicts a current sampleof the difference signal Δ(L−R) from preceding samples thereof inresponse to the related prediction coefficients. Thus, the predictors 12b-1, 12 b-2, . . . , and 12 b-n generate prediction-result signals forthe difference signal Δ(L−R) in response to the prediction coefficients,respectively. The predictors 12 b-1, 12 b-2, . . . , and 12 b-n outputthe prediction-result signals to the subtracters 13 b-1, 13 b-2, . . . ,and 13 b-n respectively. For every sample, each of the subtracters 13b-1, 13 b-2, . . . , and 13 b-n subtracts the related prediction-resultsignal from the difference signal Δ(L−R), and hence generates a signalrepresenting the prediction error between the prediction-result signaland the difference signal Δ(L−R). The subtracters 13 b-1, 13 b-2, . . ., and 13 b-n output the respective prediction-error signals to a bufferand selector 16D2.

[0053] The prediction-error signals, that is, the output signals of thesubtracters 13 b-1, 13 b-2, , and 13 b-n, are temporarily stored in amemory within the buffer and selector 16D2. The selection signalgenerator 17 produces a second selection signal. The selection signalgenerator 17 outputs the second selection signal to the buffer andselector 16D2. The second selection signal is designed to select thesmallest one from among the prediction-error signals in the memory ofthe buffer and selector 16D2 as an output signal of an optimumsubtracter (an optimum predictor) for every sub-frame. Specifically, forevery sub-frame, the selection signal generator 17 searches the memorywithin the buffer and selector 16D2 for the smallest prediction-errorsignal. In more detail, for every sub-frame, the sums of the valuesrepresented by samples of the respective prediction-error signals arecalculated. The calculated sums are compared to determine the smallestone which corresponds to the smallest prediction-error signal to beselected. The selection signal generator 17 enables the buffer andselector 16D1 to output the smallest prediction-error signal from thememory to the packing circuit 18 as the selected (L−R)-relatedprediction-error signal for every sub-frame.

[0054] In addition, the selection signal generator 17 produces a firstflag, for example, a first 5-bit flag representing the maximum numberamong the numbers of effective bits in respective samples of theselected (L+R)-related prediction-error signal which compose onesub-frame. For every sub-frame, the selection signal generator 17outputs the first flag to the packing circuit 18 and the multiplexer 19as an (L+R)-related bit-number flag.

[0055] Similarly, the selection signal generator 17 produces a secondflag, for example, a second 5-bit flag representing the maximum numberamong the numbers of effective bits in respective samples of theselected (L−R)-related prediction-error signal which compose onesub-frame. For every sub-frame, the selection signal generator 17outputs the second flag to the packing circuit 18 and the multiplexer 19as an (L−R)-related bit-number flag.

[0056] Numerals “1”, “2”, . . . , and “n” are assigned to the predictors12 a-1, 12 a-2, . . . , and 12 a-n (or the subtracters 13 a-1, 13 a-2, .. . , and 13 a-n) as identification numbers therefor, respectively. Forevery sub-frame, the selection signal generator 17 produces a third flagrepresenting the optimal predictor among the predictors 12 a-1, 12 a-2,. . . , and 12 a-n, that is, the predictor causing the selected(L+R)-related prediction-error signal. When the predetermined number “n”is equal to 9, the third flag has 3 bits. The selection signal generator17 outputs the third flag to the multiplexer 19 as an (L+R)-relatedpredictor-selection flag.

[0057] Similarly, numerals “1”, “2”, . . . , and “n” are assigned to thepredictors 12 b-1, 12 b-2, . . . , and 12 b-n (or the subtracters 13b-1, 13 b-2, . . . , and 13 b-n) as identification numbers therefor,respectively. For every sub-frame, the selection signal generator 17produces a fourth flag representing the optimal predictor among thepredictors 12 a-1, 12 a-2, . . . , and 12 a-n, that is, the predictorcausing the selected (L−R)-related prediction-error signal. When thepredetermined number “n” is equal to 9, the fourth flag has 3 bits. Theselection signal generator 17 outputs the fourth flag to the multiplexer19 as an (L−R)-related predictor-selection flag.

[0058] For every sub-frame, the packing circuit 18 packs each of samplesof the selected (L+R)-related prediction-error signal into bits, thenumber of which is equal to the maximum bit number represented by the(L+R)-related bit-number flag. The packing circuit 18 outputs everypacking-resultant sample of the selected (L+R)-related prediction-errorsignal to the multiplexer 19. In addition, for every sub-frame, thepacking circuit 18 packs each of samples of the selected (L−R)-relatedprediction-error signal into bits, the number of which is equal to themaximum bit number represented by the (L−R)-related bit-number flag. Thepacking circuit 18 outputs every packing-resultant sample of theselected (L−R)-related prediction-error signal to the multiplexer 19.

[0059] A signal generator 20 periodically produces a signal representinga predetermined frame header having, for example, 40 bits. The signalgenerator 20 outputs the frame-header signal to the multiplexer 19.

[0060] The multiplexer 19 receives the frame-header signal from thesignal generator 20 for every frame. The multiplexer 19 receives thefirst sample of the addition-result signal (L+R) and the first sample ofthe subtraction-result signal (L−R) from the buffer 10 for every frame.The multiplexer 19 receives the (L+R)-related predictor-selection flagand the (L−R)-related predictor-selection flag from the selection signalgenerator 17 for every sub-frame. The multiplexer 19 receives the(L+R)-related bit-number flag and the (L−R)-related bit-number flag fromthe selection signal generator 17 for every sub-frame. The multiplexer19 receives every packing-resultant sample of the selected (L+R)-relatedprediction-error signal and every packing-resultant sample of theselected (L−R)-related prediction-error signal from the packing circuit18. The multiplexer 19 multiplexes the received signals and flags into avariable-rate bit stream on a time sharing basis. The multiplexer 19outputs the variable-rate bit stream to the transmission line 250 (seeFIG. 1). The variable-rate bit stream represents a sequence ofvariable-bit-number frames.

[0061]FIG. 3 shows the format of every frame of the variable-rate bitstream outputted from the multiplexer 19. As shown in FIG. 3, a startingportion of every frame has the 40-bit frame header. The 40-bit frameheader is successively followed by the 25-bit first sample of theaddition-result signal (L+R), the 25-bit first sample of thesubtraction-result signal (L−R), a set of the 80 (L+R)-relatedpredictor-selection flags each having 3 bits, a set of the 80(L−R)-related predictor-selection flags each having 3 bits, a set of the80 (L+R)-related bit-number flags each having 5 bits, and a set of the80 (L−R)-related bit-number flags each having 5 bits. A set of the 80(L−R)-related bit-number flags is successively followed by a1-frame-corresonding set of the packing-resultant samples of theselected (L+R)-related prediction-error signal, and a1-frame-corresponding set of the packing-resultant samples of theselected (L−R)-related prediction-error signal. Since 80 sub-framescompose one frame and the number of bits of every packing-resultantsample varies from sub-frame to sub-frame, a 1-frame-corresponding setof the packing-resultant samples of the selected (L+R)-relatedprediction-error signal has a variable bit number. Also, a1-frame-corresponding set of the packing-resultant samples of theselected (L−R)-related prediction-error signal has a variable bitnumber.

[0062] The rate of compression of the variable-rate bit stream relativeto the pair of the left-channel digital audio signal “L” and theright-channel digital audio signal “R” is equal to, for example, 59%.

[0063] As shown in FIG. 4, the lossless decoder 3D includes ademultiplexer 21 which receives the variable-rate bit stream from thetransmission line 250 (see FIG. 1). A first portion of the demultiplexer21 detects every frame header in the received variable-rate bit stream.For every frame, a second portion of the demultiplexer 21 demultiplexes,in response to the detected frame header, the received variable-rate bitstream into the first sample of the addition-result signal (L+R), thefirst sample of the subtraction-result signal (L−R), a set of the 80(L+R)-related predictor-selection flags, a set of the 80 (L−R)-relatedpredictor-selection flags, a set of the 80 (L+R)-related bit-numberflags, a set of the 80 (L−R)-related bit-number flags, a1-frame-corresponding set of the packing-resultant samples of theselected (L+R)-related prediction-error signal, and a1-frame-corresponding set of the packing-resultant samples of theselected (L−R)-related prediction-error signal.

[0064] In the lossless decoder 3D, the demultiplexer 21 outputs thefirst sample of the addition-result signal (L+R) to an accumulationcircuit 25 a for every frame. The demultiplexer 21 outputs the firstsample of the subtraction-result signal (L−R) to an accumulation circuit25 b for every frame. The demultiplexer 21 outputs every (L+R)-relatedpredictor-selection flag to predictors 24 a-1, 24 a-2, . . . , and 24a-n. The demultiplexer 21 outputs every (L−R)-relatedpredictor-selection flag to predictors 24 b-1, 24 b-2, . . . , and 24b-n. The demultiplexer 21 outputs every (L+R)-related bit-number flagand every (L−R)-related bit-number flag to a de-packing circuit 22. Thedemultiplexer 21 outputs every packing-resultant sample of the selected(L+R)-related prediction-error signal and every packing-resultant sampleof the selected (L−R)-related prediction-error signal to the de-packingcircuit 22.

[0065] For every sub-frame, the de-packing circuit 22 implements theunpacking of the packing-resultant samples of the selected (L+R)-relatedprediction-error signal in response to the (L+R)-related bit-numberflag. The de-packing circuit 22 outputs the resultant (L+R)-relatedprediction-error signal to an addition circuit 23 a. For everysub-frame, the de-packing circuit 22 implements the unpacking of thepacking-resultant samples of the selected (L−R)-related prediction-errorsignal in response to the (L−R)-related bit-number flag. The de-packingcircuit 22 outputs the resultant (L−R)-related prediction-error signalto an addition circuit 23 b.

[0066] The predictors 24 a-1, 24 a-2, . . . , and 24 a-n have the samecharacteristics as those of the predictors 12 a-1, 12 a-2, . . . , and12 a-n in the lossless encoder 2D, respectively. For every sub-frame,one of the predictors 24 a-1, 24 a-2, . . . , and 24 a-n is selected inresponse to the (L+R)-related predictor-selection flag. Specifically,one of the predictors 24 a-1, 24 a-2, . . . , and 24 a-n is selectedwhich has the same characteristic as the encoder-side predictor used forthe sub-frame of interest. The selected predictor generates aprediction-result signal in response to an output signal of the additioncircuit 23 a. The selected predictor is enabled to output theprediction-result signal to the addition circuit 23 a. The additioncircuit 23 a adds the (L+R)-related prediction-error signal and theprediction-result signal into the difference signal Δ(L+R) which isequal to the DPCM signal Δ(L+R) outputted from the differencecalculation circuit 11D1 in the lossless encoder 2D. The additioncircuit 23 a outputs the difference signal Δ(L+R) to the accumulationcircuit 25 a and the predictors 24 a-1, 24 a-2, . . . , and 24 a-n.

[0067] The predictors 24 b-1, 24 b-2, . . . , and 24 b-n have the samecharacteristics as those of the predictors 12 b-1, 12 b-2, . . . , and12 b-n in the lossless encoder 2D, respectively. For every sub-frame,one of the predictors 24 b-1, 24 b-2, . . . , and 24 b-n is selected inresponse to the (L−R)-related predictor-selection flag. Specifically,one of the predictors 24 b-1, 24 b-2, . . . , and 24 b-n is selectedwhich has the same characteristic as the encoder-side predictor used forthe sub-frame of interest. The selected predictor generates aprediction-result signal in response to an output signal of the additioncircuit 23 b. The selected predictor is enabled to output theprediction-result signal to the addition circuit 23 b. The additioncircuit 23 b adds the (L−R)-related prediction-error signal and theprediction-result signal into the difference signal Δ(L−R) which isequal to the DPCM signal Δ(L−R) outputted from the differencecalculation circuit 11D2 in the lossless encoder 2D. The additioncircuit 23 b outputs the difference signal Δ(L−R) to the accumulationcircuit 25 b and the predictors 24 b-1, 24 b-2, . . . , and 24 b-n.

[0068] The accumulation circuit 25 a accumulates samples of thedifference signal Δ(L+R) with respect to the first sample of theaddition-result signal (L+R) in a frame, thereby reproducing a sequenceof samples of the addition-result signal (L+R) which is equal to theoutput signal of the addition circuit la in the channel correlationcircuit “A” of the audio signal encoding apparatus 100. The accumulationcircuit 25 a outputs the reproduced addition-result signal (L+R) to thechannel correlation circuit “B” (see FIG. 1).

[0069] The accumulation circuit 25 b accumulates samples of thedifference signal Δ(L−R) with respect to the first sample of thesubtraction-result signal (L−R) in a frame, thereby reproducing asequence of samples of the subtraction-result signal (L−R) which isequal to the output signal of the subtraction circuit 1 b in the channelcorrelation circuit “A” of the audio signal encoding apparatus 100. Theaccumulation circuit 25 b outputs the reproduced subtraction-resultsignal (L−R) to the channel correlation circuit “B” (see FIG. 1).

[0070] With reference back to FIG. 1, the channel correlation circuit“B” includes an addition circuit 4 a, a subtraction circuit 4 b, and ½dividers 5 a and 5 b. The addition circuit 4 a receives theaddition-result signal (L+R) and the subtraction-result signal (L−R)from the lossless decoder 3D. The addition circuit 4 a adds theaddition-result signal (L+R) and the subtraction-result signal (L−R)into a signal 2L. The addition circuit 4 a outputs the signal 2L to thedivider 5 a. The divider 5 a halves the signal 2L, thereby reproducingthe original left-channel digital audio signal “L”. The divider 5 aoutputs the reproduced left-channel digital audio signal “L”. Thesubtraction circuit 4 b receives the addition-result signal (L+R) andthe subtraction-result signal (L−R) from the lossless decoder 3D. Thesubtraction circuit 4 b subtracts the subtraction-result signal (L−R)from the addition-result signal (L+R), thereby generating a signal 2R.The subtraction circuit 4 b outputs the signal 2R to the divider 5 b.The divider 5 b halves the signal 2R, thereby reproducing the originalright-channel digital audio signal “R”. The divider 5 b outputs thereproduced right-channel digital audio signal “R”.

Second Embodiment

[0071] A second embodiment of this invention is similar to the firstembodiment thereof except for design changes mentioned later.

[0072]FIG. 5 shows a lossless encoder in the second embodiment of thisinvention which is a modification of the lossless encoder 2D in thefirst embodiment of this invention.

[0073] The lossless encoder of FIG. 5 includes prediction circuits 15Aand 15S, a buffer and selector 16A, and a buffer and selector 16S. Theprediction circuit 15A is similar in structure to the prediction circuit15D1. The prediction circuit 15S is similar in structure to theprediction circuit 15D2. The buffer and selector 16A is similar instructure to the buffer and selector 16D1. The buffer and selector 16Sis similar in structure to the buffer and selector 16D2.

[0074] The prediction circuit 15A receives the PCM addition-resultsignal (L+R) from the buffer 10. The prediction circuit 15A generates aset of PCM prediction-error signals in response to the PCMaddition-result signal (L+R). The prediction circuit 15A outputs the PCMprediction-error signals to the buffer and selector 16A. The PCMprediction-error signals are temporarily stored in a memory within thebuffer and selector 16A. The selection signal generator 17 outputs aselection signal to the buffer and selector 16A. The selection signal isdesigned to select the smallest one from among the PCM prediction-errorsignals in the memory of the buffer and selector 16A as an output signalof an optimum subtracter (an optimum predictor) for every sub-frame.Specifically, for every sub-frame, the selection signal generator 17searches the memory within the buffer and selector 16A for the smallestPCM prediction-error signal. The smallest PCM prediction-error signal isthe selected PCM (L+R)-related prediction-error signal.

[0075] In addition, the selection signal generator 17 produces an(L+R)-related bit-number flag representing the maximum number among thenumbers of effective bits in respective samples of the selected PCM(L+R)-related prediction-error signal which compose one sub-frame. Forevery sub-frame, the selection signal generator 17 outputs the(L+R)-related bit-number flag to the packing circuit 18 and themultiplexer 19. Also, for every sub-frame, the selection signalgenerator 17 produces an (L+R)-related predictor-selection flagrepresenting the optimal predictor causing the selected PCM(L+R)-related prediction-error signal. The selection signal generator 17outputs the (L+R)-related predictor-selection flag to the multiplexer19.

[0076] The prediction circuit 15S receives the PCM subtraction-resultsignal (L−R) from the buffer 10. The prediction circuit 15S generates aset of PCM prediction-error signals in response to the PCMsubtraction-result signal (L−R). The prediction circuit 15S outputs thePCM prediction-error signals to the buffer and selector 16S. The PCMprediction-error signals are temporarily stored in a memory within thebuffer and selector 16S. The selection signal generator 17 outputs aselection signal to the buffer and selector 16S. The selection signal isdesigned to select the smallest one from among the PCM prediction-errorsignals in the memory of the buffer and selector 16S as an output signalof an optimum subtracter (an optimum predictor) for every sub-frame.Specifically, for every sub-frame, the selection signal generator 17searches the memory within the buffer and selector 16S for the smallestPCM prediction-error signal. The smallest PCM prediction-error signal isthe selected PCM (L−R)-related prediction-error signal.

[0077] In addition, the selection signal generator 17 produces an(L−R)-related bit-number flag representing the maximum number among thenumbers of effective bits in respective samples of the selected PCM(L−R)-related prediction-error signal which compose one sub-frame. Forevery sub-frame, the selection signal generator 17 outputs the(L−R)-related bit-number flag to the packing circuit 18 and themultiplexer 19. Also, for every sub-frame, the selection signalgenerator 17 produces an (L−R)-related predictor-selection flagrepresenting the optimal predictor causing the selected PCM(L−R)-related prediction-error signal. The selection signal generator 17outputs the (L−R)-related predictor-selection flag to the multiplexer19.

[0078] For every sub-frame, the selection signal generator 17 searchesthe memory within the buffer and selector 16D1 for the smallest DPCMprediction-error signal. The smallest DPCM prediction-error signal isthe selected DPCM (L+R)-related prediction-error signal. Also, for everysub-frame, the selection signal generator 17 searches the memory withinthe buffer and selector 16D2 for the smallest DPCM prediction-errorsignal. The smallest DPCM prediction-error signal is the selected DPCM(L−R)-related prediction-error signal.

[0079] Furthermore, for every sub-frame, the selection signal generator17 decides which of the pair of the selected PCM (L+R)-relatedprediction-error signal and the selected PCM (L−R)-relatedprediction-error signal, and the pair of the selected DPCM (L+R)-relatedprediction-error signal and the selected DPCM (L−R)-relatedprediction-error signal is higher in compression rate by comparing thevalues represented thereby. The selection signal generator 17 selectsthe higher-compression pair of the (L+R)-related prediction-error signaland the (L−R)-related prediction-error signal. The selection signalgenerator 17 enables the higher-compression pair of the (L+R)-relatedprediction-error signal and the (L−R)-related prediction-error signal tobe outputted to the packing circuit 18.

[0080] For every sub-frame, the selection signal generator 17 produces aprediction-circuit-selection flag representing which of the PCMprediction-error signal pair and the DPCM prediction-error signal pairis selected. The selection signal generator 17 outputs theprediction-circuit-selection flag to the multiplexer 19. The multiplexer19 adds the prediction-circuit-selection flag into the variable-rate bitstream.

[0081]FIG. 6 shows a lossless decoder in the second embodiment of thisinvention which is a modification of the lossless decoder 3D in thefirst embodiment of this invention. The lossless decoder of FIG. 6includes selectors 26 a and 26 b. The demultiplexer 21 separates everyprediction-circuit-selection flag from the variable-rate bit stream. Thedemultiplexer 21 feeds the prediction-circuit-selection flag to theselectors 26 a and 26 b. When the prediction-circuit-selection flagindicates that the DPCM prediction-error signal pair is selected, theselector 26 a selects the output signal of the accumulation circuit 25 aand the selector 26 b selects the output signal of the accumulationcircuit 25 b. When the prediction-circuit-selection flag indicates thatthe PCM prediction-error signal pair is selected, the selector 26 aselects the output signal of the addition circuit 23 a and the selector26 b selects the output signal of the addition circuit 23 b. The signalselected by the selector 26 a constitutes the reproduced addition-resultsignal (L+R). The signal selected by the selector 26 b constitutes thereproduced subtraction-result signal (L−R).

Third Embodiment

[0082] A third embodiment of this invention is similar to the firstembodiment thereof except for design changes mentioned later. FIG. 7shows an audio signal encoding apparatus in the third embodiment of thisinvention which is a modification of the audio signal encoding apparatus100 in the first embodiment of this invention.

[0083] The audio signal encoding apparatus of FIG. 7 includes a bufferin which a left-channel digital audio signal “L” and a right-channeldigital audio signal “R” are temporarily stored. The left-channeldigital audio signal “L” is fed from the buffer 10 to a predictioncircuit 15L and a channel correlation circuit “A”. The right-channeldigital audio signal “R” is fed from the buffer 10 to a predictioncircuit 15R and the channel correlation circuit “A”. For every frame,the first sample of the left-channel digital audio signal “L” and thefirst sample of the right-channel digital audio signal “R” aretransmitted from the buffer 10 to the multiplexer 19.

[0084] An addition circuit la in the channel correlation circuit “A”adds the left-channel digital audio signal “L” and the right-channeldigital audio signal “R” into a PCM addition-result signal (L+R). Theaddition circuit la outputs the PCM addition-result signal (L+R) to aprediction circuit 15A and a difference calculation circuit 11D1. Forevery frame, the first sample of the PCM addition-result signal (L+R) istransmitted from the addition circuit 1 a to the multiplexer 19. Asubtraction circuit 1 b in the channel correlation circuit “A” subtractsthe right-channel digital audio signal “R” from the left-channel digitalaudio signal “L”, thereby generating a PCM subtraction-result signal(L−R). The subtraction circuit 1 b outputs the PCM subtraction-resultsignal (L−R) to a prediction circuit 15S and a difference calculationcircuit 11D2. For every frame, the first sample of the PCMsubtraction-result signal (L−R) is transmitted from the subtractioncircuit 1 b to the multiplexer 19.

[0085] The difference calculation circuit 11D1 generates a DPCM signalΔ(L+R) from the PCM addition-result signal (L+R). The differencecalculation circuit 11D1 outputs the DPCM signal Δ(L+R) to a predictioncircuit 15D1. The difference calculation circuit 11D2 generates a DPCMsignal Δ(L−R) from the PCM subtraction-result signal (L−R). Thedifference calculation circuit 11D2 outputs the DPCM signal Δ(L−R) to aprediction circuit 15D2.

[0086] The prediction circuits 15A and 15L are similar in structure tothe prediction circuit 15D1. The prediction circuits 15R and 15S aresimilar in structure to the prediction circuit 15D2. The predictioncircuit 15A is followed by a buffer and selector 16A. The predictioncircuit 15L is followed by a buffer and selector 16L. The predictioncircuit 15R is followed by a buffer and selector 16R. The predictioncircuit 15S is followed by a buffer and selector 16S. The predictioncircuit 15D1 is followed by a buffer and selector 16D1, the predictioncircuit 15D2 is followed by a buffer and selector 16D2. The buffer andselector 16A is similar in structure to the buffer and selector 16D1.The buffer and selector 16L is similar in structure to the buffer andselector 16D1. The buffer and selector 16R is similar in structure tothe buffer and selector 16D2. The buffer and selector 16S is similar instructure to the buffer and selector 16D2.

[0087] The prediction circuit 15A receives the PCM addition-resultsignal (L+R) from the addition circuit la in the channel correlationcircuit “A”. The prediction circuit 15A generates a set of PCMprediction-error signals in response to the PCM addition-result signal(L+R). The prediction circuit 15A outputs the PCM prediction-errorsignals to the buffer and selector 16A. The PCM prediction-error signalsare temporarily stored in a memory within the buffer and selector 16A.The selection signal generator 17 outputs a selection signal to thebuffer and selector 16A. The selection signal is designed to select thesmallest one from among the PCM prediction-error signals in the memoryof the buffer and selector 16A as an output signal of an optimumsubtracter (an optimum predictor) for every sub-frame. Specifically, forevery sub-frame, the selection signal generator 17 searches the memorywithin the buffer and selector 16A for the smallest PCM prediction-errorsignal. The smallest PCM prediction-error signal is the selected PCM(L+R)-related prediction-error signal.

[0088] In addition, the selection signal generator 17 produces an(L+R)-related bit-number flag representing the maximum number among thenumbers of effective bits in respective samples of the selected PCM(L+R)-related prediction-error signal which compose one sub-frame. Forevery sub-frame, the selection signal generator 17 outputs the(L+R)-related bit-number flag to the packing circuit 18 and themultiplexer 19. Also, for every sub-frame, the selection signalgenerator 17 produces an (L+R)-related predictor-selection flagrepresenting the optimal predictor causing the selected PCM(L+R)-related prediction-error signal. The selection signal generator 17outputs the (L+R)-related predictor-selection flag to the multiplexer19.

[0089] The prediction circuit 15S receives the PCM subtraction-resultsignal (L−R) from the subtraction circuit 1 b in the channel correlationcircuit “A”. The prediction circuit 15S generates a set of PCMprediction-error signals in response to the PCM subtraction-resultsignal (L−R). The prediction circuit 15S outputs the PCMprediction-error signals to the buffer and selector 16S. The PCMprediction-error signals are temporarily stored in a memory within thebuffer and selector 16S. The selection signal generator 17 outputs aselection signal to the buffer and selector 16S. The selection signal isdesigned to select the smallest one from among the PCM prediction-errorsignals in the memory of the buffer and selector 16S as an output signalof an optimum subtracter (an optimum predictor) for every sub-frame.Specifically, for every sub-frame, the selection signal generator 17searches the memory within the buffer and selector 16S for the smallestPCM prediction-error signal. The smallest PCM prediction-error signal isthe selected PCM (L−R)-related prediction-error signal.

[0090] In addition, the selection signal generator 17 produces an(L−R)-related bit-number flag representing the maximum number among thenumbers of effective bits in respective samples of the selected PCM(L−R)-related prediction-error signal which compose one sub-frame. Forevery sub-frame, the selection signal generator 17 outputs the(L−R)-related bit-number flag to the packing circuit 18 and themultiplexer 19. Also, for every sub-frame, the selection signalgenerator 17 produces an (L−R)-related predictor-selection flagrepresenting the optimal predictor causing the selected PCM(L−R)-related prediction-error signal. The selection signal generator 17outputs the (L−R)-related predictor-selection flag to the multiplexer19.

[0091] The prediction circuit 15L receives the left-channel digitalaudio signal “L” from the buffer 10. The prediction circuit 15Lgenerates a set of original-L prediction-error signals in response tothe left-channel digital audio signal “L”. The prediction circuit 15Loutputs the original-L prediction-error signals to the buffer andselector 16L. The original-L prediction-error signals are temporarilystored in a memory within the buffer and selector 16L. The selectionsignal generator 17 outputs a selection signal to the buffer andselector 16L. The selection signal is designed to select the smallestone from among the original-L prediction-error signals in the memory ofthe buffer and selector 16L as an output signal of an optimum subtracter(an optimum predictor) for every sub-frame. Specifically, for everysub-frame, the selection signal generator 17 searches the memory withinthe buffer and selector 16L for the smallest original-L prediction-errorsignal. The smallest original-L prediction-error signal is the selectedoriginal-L prediction-error signal.

[0092] In addition, the selection signal generator 17 produces anL-related bit-number flag representing the maximum number among thenumbers of effective bits in respective samples of the selectedoriginal-L prediction-error signal which compose one sub-frame. Forevery sub-frame, the selection signal generator 17 outputs the L-relatedbit-number flag to the packing circuit 18 and the multiplexer 19. Also,for every sub-frame, the selection signal generator 17 produces anL-related predictor-selection flag representing the optimal predictorcausing the selected original-L prediction-error signal. The selectionsignal generator 17 outputs the L-related predictor-selection flag tothe multiplexer 19.

[0093] The prediction circuit 15R receives the right-channel digitalaudio signal “R” from the buffer 10. The prediction circuit 15Rgenerates a set of original-R prediction-error signals in response tothe right-channel digital audio signal “R”. The prediction circuit 15Routputs the original-R prediction-error signals to the buffer andselector 16R. The original-R prediction-error signals are temporarilystored in a memory within the buffer and selector 16R. The selectionsignal generator 17 outputs a selection signal to the buffer andselector 16R. The selection signal is designed to select the smallestone from among the original-R prediction-error signals in the memory ofthe buffer and selector 16R as an output signal of an optimum subtracter(an optimum predictor) for every sub-frame. Specifically, for everysub-frame, the selection signal generator 17 searches the memory withinthe buffer and selector 16R for the smallest original-R prediction-errorsignal. The smallest original-R prediction-error signal is the selectedoriginal-R prediction-error signal.

[0094] In addition, the selection signal generator 17 produces anR-related bit-number flag representing the maximum number among thenumbers of effective bits in respective samples of the selectedoriginal-R prediction-error signal which compose one sub-frame. Forevery sub-frame, the selection signal generator 17 outputs the R-relatedbit-number flag to the packing circuit 18 and the multiplexer 19. Also,for every sub-frame, the selection signal generator 17 produces anR-related predictor-selection flag representing the optimal predictorcausing the selected original-R prediction-error signal. The selectionsignal generator 17 outputs the R-related predictor-selection flag tothe multiplexer 19.

[0095] For every sub-frame, the selection signal generator 17 searchesthe memory within the buffer and selector 16D1 for the smallest DPCMprediction-error signal. The smallest DPCM prediction-error signal isthe selected DPCM (L+R)-related prediction-error signal. Also, for everysub-frame, the selection signal generator 17 searches the memory withinthe buffer and selector 16D2 for the smallest DPCM prediction-errorsignal. The smallest DPCM prediction-error signal is the selected DPCM(L−R)-related prediction-error signal.

[0096] Furthermore, for every sub-frame, the selection signal generator17 decides which of the pair of the original-L prediction-error signaland the original-R prediction-error signal, the pair of the selected PCM(L+R)-related prediction-error signal and the selected PCM (L−R)-relatedprediction-error signal, and the pair of the selected DPCM (L+R)-relatedprediction-error signal and the selected DPCM (L−R)-relatedprediction-error signal is the highest in compression rate by comparingthe values represented thereby. The selection signal generator 17selects the highest-compression pair of the prediction-error signals.The selection signal generator 17 enables the highest-compression pairof the prediction-error signals to be outputted to the packing circuit18.

[0097] For every sub-frame, the selection signal generator 17 produces aprediction-circuit-selection flag representing which of the originalprediction-error signal pair, the PCM prediction-error signal pair, andthe DPCM prediction-error signal pair is selected. The selection signalgenerator 17 outputs the prediction-circuit-selection flag to themultiplexer 19. The multiplexer 19 adds the prediction-circuit-selectionflag into the variable-rate bit stream.

[0098]FIG. 8 shows an audio signal decoding apparatus in the thirdembodiment of this invention which is a modification of the audio signaldecoding apparatus 200 in the first embodiment of this invention. Theaudio signal decoding apparatus of FIG. 8 includes selectors 26 a, 26 b,27 a, and 27 b. The demultiplexer 21 separates everyprediction-circuit-selection flag from the variable-rate bit stream. Thedemultiplexer 21 feeds the prediction-circuit-selection flag to theselectors 26 a, 26 b, 27 a, and 27 b. When theprediction-circuit-selection flag indicates that the DPCMprediction-error signal pair is selected, the selector 26 a selects theoutput signal of the accumulation circuit 25 a and the selector 26 bselects the output signal of the accumulation circuit 25 b. When theprediction-circuit-selection flag indicates that the PCM predictionerror signal pair is selected, the selector 26 a selects the outputsignal of the addition circuit 23 a and the selector 26 b selects theoutput signal of the addition circuit 23 b. The signal selected by theselector 26 a constitutes the reproduced addition-result signal (L+R).The signal selected by the selector 26 b constitutes the reproducedsubtraction-result signal (L−R). The reproduced addition-result signal(L+R) and the reproduced subtraction-result signal (L−R) are fed to thechannel correlation circuit “B”.

[0099] When the prediction-circuit-selection flag indicates that theoriginal prediction-error signal pair is selected, the selector 27 aselects the output signal of the addition circuit 23 a and the selector27 b selects the output signal of the addition circuit 23 b. Otherwise,the selector 27 a selects the output signal of the divider 5 a in thechannel correlation circuit “B” and the selector 27 b selects the outputsignal of the divider 5 b in the channel correlation circuit “B”. Thesignal selected by the selector 27 a constitutes the reproducedleft-channel digital audio signal “L”. The signal selected by theselector 27 b constitutes the reproduced right-channel digital audiosignal “R”.

Fourth Embodiment

[0100] A fourth embodiment of this invention is similar to one of thefirst, second, and third embodiments thereof except for design changesmentioned later.

[0101] With reference to FIG. 9, the fourth embodiment of this inventionincludes a DVD-audio encoder 300 which follows the audio signal encodingapparatus 100. The DVD-audio encoder 300 converts the output signal ofthe audio signal encoding apparatus (that is, the variable-rate bitstream) into a DVD-audio-format signal. The DVD-audio encoder 300outputs the DVD-audio-format signal to a DVD drive 302. A writer in theDVD drive 302 records the DVD-audio-format signal on a DVD-audio disc304.

[0102] A reader in the DVD drive 302 reproduces the DVD-audio-formatsignal from the DVD-audio disc 304. The reader in the DVD drive 302outputs the reproduced signal to a DVD-audio decoder 306. The DVD-audiodecoder 306 recovers the variable-rate bit stream from the reproducedsignal. The DVD-audio decoder 306 outputs the recovered variable-ratebit stream to the audio signal decoding apparatus 200.

[0103] The DVD-audio-format signal generated by the DVD-audio encoder300 has a stream of packs including audio packs. As shown in FIG. 10,each audio pack has a sequence of 4-byte pack start information, 6-byteSCR (system clock reference) information, 3-byte mux rate information,1-byte stuffing data, and 2,034-byte packet-form user data. Thus, eachaudio pack has 2,048 bytes. In each audio pack, pack start information,SCR information, mux rate information, and stuffing data compose a14-byte pack header. SCR information in each audio pack serves as a timestamp. In each audio pack, 2,034-byte packet-form user data contains aportion of the variable-rate bit stream.

[0104] A time stamp in a first audio pack among audio packs related toone title is set to “1”. Time stamps in second and later audio packsrelated to the same title are set to serial numbers “2”, “3”, “4”, . . ., respectively. The serially-numbered time stamps make it possible tomanage times of audio packs related to the same title.

[0105] As shown in FIG. 11, one audio pack has a 14-byte pack header andan audio packet. The pack header is followed by the audio packet. Theaudio packet has a sequence of a packet header, a private header, andaudio data (linear PCM audio data). The packet header has 9 bytes, 14bytes, or 17 bytes. The audio data has 1 byte to 2,011 bytes. The audiodata is a portion of the variable-rate bit stream.

[0106] As shown in FIG. 11, the private header has a sequence of 1-bytesub stream ID (identification) information, 2-byte information of anUPC/EAN-ISRC (Universal Product Code/European ArticleNumber-International Standard Recording Code) number and UPC/EAN-ISRCdata, 1-byte information of the private header length, a 2-byte firstaccess unit pointer, 8-byte audio data information ADI, and 0 to 7stuffing bytes.

Fifth Embodiment

[0107] A fifth embodiment of this invention is similar to one of thefirst, second, and third embodiments thereof except for design changesmentioned later.

[0108] With reference to FIG. 12, the fifth embodiment of this inventionincludes a packeting processor 350 which follows the audio signalencoding apparatus 100. The packeting processor 350 encodes the outputsignal of the audio signal encoding apparatus (that is, thevariable-rate bit stream) into a packet stream. The packeting processor350 transmits the packet stream to a communication network (or acommunication line) 360.

[0109] A de-packeting processor 370 receives the packet stream from thecommunication network 360. The de-packeting processor 370 decodes thepacket stream into the variable-rate bit stream. The de-packetingprocessor 370 outputs the variable-rate bit stream to the audio signaldecoding apparatus 200.

[0110] The packeting processor 350 operates in accordance with a controlprogram stored in its internal ROM or another memory. FIG. 13 is aflowchart of a segment of the control program. As shown in FIG. 13, afirst step S41 of the program segment divides the variable-rate bitstream into basic packets each having a predetermined number of bits. Astep S42 following the step S41 adds headers to the starting ends of thebasic packets to change the basic packets to final packets respectively.Generally, the added headers include destination addresses. A step S43subsequent to the step S42 sequentially transmits the final packets tothe communication network 360.

[0111] The de-packeting processor 370 operates in accordance with a,control program stored in its internal ROM or another memory. FIG. 14 isa flowchart of a segment of the control program. As shown in FIG. 14, afirst step S51 of the program segment removes headers from receivedpackets. A step S52 following the step S51 recovers the variable-ratebit stream from the header-less packets. A step S53 subsequent to thestep S52 stores the recovered variable-rate bit stream into a buffermemory provided in the de-packeting processor 370. The variable-rate bitstream is transmitted from the buffer memory to the audio signaldecoding apparatus 200.

Sixth Embodiment

[0112]FIG. 15 shows a sixth embodiment of this invention which issimilar to the first embodiment thereof except for design changesindicated hereinafter.

[0113] The embodiment of FIG. 15 includes a lossless encoder 2E and alossless decoder 3E which replace the lossless encoder 2D and the lossdecoder 3D (see FIG. 1) respectively. The lossless encoder 2E follows achannel correlation circuit “A”. The lossless decoder 3E precedes achannel correlation circuit “B”.

[0114] The embodiment of FIG. 15 includes a channel correlation circuitsA2 and B2. The channel correlation circuit A2 precedes the losslessencoder 2E. The channel correlation circuit B2 follows the losslessdecoder 3E.

[0115] An encoder side of the embodiment of FIG. 15 receives amulti-channel digital audio signal composed of a left-channel digitalaudio signal “L”, a right-channel digital audio signal “R”, a leftsurround signal “SL”, and a right surround signal “SR”. Themulti-channel digital audio signal is reproduced from a digitalrecording medium such as a DVD-audio (a digital versatile disc audio).The left-channel digital audio signal “L” and the right-channel digitalaudio signal “R” are processed by the channel correlation circuit “A”into an addition-result signal (L+R) and a subtraction-result signal(L−R). The addition-result signal (L+R) and the subtraction-resultsignal (L−R) are fed to the lossless encoder 2E. The left surroundsignal “SL” and the right surround signal “SR” are processed by thechannel correlation circuit A2 into an addition-result signal (SL+SR)and a subtraction-result signal (SL−SR). The addition-result signal(SL+SR) and the subtraction-result signal (SL−SR) are fed to thelossless encoder 2E.

[0116] The channel correlation circuit A2 includes an addition circuit 1a 2 and a subtraction circuit 1 b 2. The addition circuit 1 a 2 receivesthe left surround signal “SL” and the right surround signal “SR”. Theaddition circuit 1 a 2 adds the left surround signal “SL” and the rightsurround signal “SR” into an addition-result signal (SL+SR). Theaddition circuit 1 a 2 outputs the addition-result signal (SL+SR) to thelossless encoder 2E. The subtraction circuit 1 b 2 receives the leftsurround signal “SL” and the right surround signal “SR”. The subtractioncircuit 1 b 2 subtracts the right surround signal “SR” from the leftsurround signal “SL”, thereby generating a subtraction-result signal(SL−SR). The subtraction circuit 1 b 2 outputs the subtraction-resultsignal (SL−SR) to the lossless encoder 2E.

[0117] The lossless encoder 2E encodes the addition-result signal (L+R)and the subtraction-result signal (L−R) into a first encoding-resultantsignal as the lossless encoder 2D in FIG. 1 does. Similarly, thelossless encoder 2E encodes the addition-result signal (SL+SR) and thesubtraction-result signal (SL−SR) into a second encoding-resultantsignal. The lossless encoder 2E combines the first encoding-resultantsignal and the second encoding-resultant signal into a variable-rate bitstream representing a sequence of variable-bit-number frames. Thelossless encoder 2E outputs the variable-rate bit stream to atransmission line 250.

[0118]FIG. 16 shows the format of every frame of the variable-rate bitstream outputted from the lossless encoder 2E. As shown in FIG. 16, astarting portion of every frame has a frame header. The frame header issuccessively followed by a first data section and a second data section.The first data section is loaded with information related to theaddition-result signal (L+R) and the subtraction-result signal (L−R).The second data section is loaded with information related to theaddition-result signal (SL+SR) and the subtraction-result signal(SL−SR).

[0119] With reference back to FIG. 15, the lossless decoder 3E receivesthe variable-rate bit stream from the transmission line 250. Thelossless decoder 3E divides the variable-rate bit stream into firstinformation related to the addition-result signal (L+R) and thesubtraction-result signal (L−R), and second information related to theaddition-result signal (SL+SR) and the subtraction-result signal(SL−SR). The lossless decoder 3E decodes the first information into theaddition-result signal (L+R) and the subtraction-result signal (L−R) asthe lossless decoder 3D in FIG. 1 does. The lossless decoder 3E outputsthe addition-result signal (L+R) and the subtraction-result signal (L−R)to the channel correlation circuit “B”. Similarly, the lossless decoder3E decodes the second information into the addition-result signal(SL+SR) and the subtraction-result signal (SL−SR). The lossless decoder3E outputs the addition-result signal (SL+SR) and the subtraction-resultsignal (SL−SR) to the channel correlation circuit B2.

[0120] The channel correlation circuit B includes an addition circuit 4a 2, a subtraction circuit 4 b 2, and ½ dividers 5 a 2 and 5 b 2. Theaddition circuit 4 a 2 receives the addition-result signal (SL+SR) andthe subtraction-result signal (SL−SR) from the lossless decoder 3E. Theaddition circuit 4 a 2 adds the addition-result signal (SL+SR) and thesubtraction-result signal (SL−SR) into a signal 2SL. The additioncircuit 4 a 2 outputs the signal 2SL to the divider 5 a 2. The divider 5a 2 halves the signal 2SL, thereby reproducing the original leftsurround signal “SL”. The divider 5 a 2 outputs the reproduced leftsurround signal “SL”. The subtraction circuit 4 b 2 receives theaddition-result signal (SL+SR) and the subtraction-result signal (SL−SR)from the lossless decoder 3E. The subtraction circuit 4 b 2 subtractsthe subtraction-result signal (SL−SR) from the addition-result signal(SL+SR), thereby generating a signal 2SR. The subtraction circuit 4 b 2outputs the signal 2SR to the divider 5 b 2. The divider 5 b 2 halvesthe signal 2SR, thereby reproducing the original right surround signal“SR”. The divider 5 b 2 outputs the reproduced right surround signal“SR”.

Seventh Embodiment

[0121]FIG. 17 shows a seventh embodiment of this invention which issimilar to the first embodiment thereof except for design changesindicated hereinafter.

[0122] The embodiment of FIG. 17 includes a lossless encoder 2F and alossless decoder 3F which replace the lossless encoder 2D and the lossdecoder 3D (see FIG. 1) respectively. The lossless encoder 2F follows achannel correlation circuit “A”. The lossless decoder 3F precedes achannel correlation circuit “B”.

[0123] An encoder side of the embodiment of FIG. 17 receives amulti-channel digital audio signal composed of a left-channel digitalaudio signal “L”, a right-channel digital audio signal “R”, a centersignal “C”, a left surround signal “SL”, a right surround signal “SR”,and a low frequency effect signal “LFE”. The multi-channel digital audiosignal is reproduced from a digital recording medium such as a DVD-audio(a digital versatile disc audio). The left-channel digital audio signal“L” and the right-channel digital audio signal “R” are processed by thechannel correlation circuit “A” into an addition-result signal (L+R) anda subtraction-result signal (L−R). The addition-result signal (L+R) andthe subtraction-result signal (L−R) are fed to the lossless encoder 2F.The center signal “C”, the left surround signal “SL”, the right surroundsignal “SR”, and the low frequency effect signal “LFE” are directlyapplied to the lossless encoder 2F.

[0124] The lossless encoder 2E encodes the addition-result signal (L+R)and the subtraction-result signal (L−R) into a first encoding-resultantsignal as the lossless encoder 2D in FIG. 1 does. Also, the losslessencoder 2F encodes the center signal “C”, the left surround signal “SL”,the right surround signal “SR”, and the low frequency effect signal“LFE” into second, third, fourth, and fifth encoding-resultant signals,respectively. The lossless encoder 2F combines the first, second, third,fourth, and fifth encoding-resultant signals into a variable-rate bitstream representing a sequence of variable-bit-number frames. Thelossless encoder 2F outputs the variable-rate bit stream to atransmission line 250.

[0125]FIG. 18 shows the format of every frame of the variable-rate bitstream outputted from the lossless encoder 2F. As shown in FIG. 18, astarting portion of every frame has a frame header. The frame header issuccessively followed by a first data section and a second data section.The first data section is loaded with information related to theaddition-result signal (L+R) and the subtraction-result signal (L−R).The second data section is loaded with information related to the centersignal “C”, the left surround signal “SL”, the right surround signal“SR”, and the low frequency effect signal “LFE”.

[0126] With reference back to FIG. 17, the lossless decoder 3F receivesthe variable-rate bit stream from the transmission line 250. Thelossless decoder 3F divides the variable-rate bit stream into firstinformation related to the addition-result signal (L+R) and thesubtraction-result signal (L−R), and second information related to thecenter signal “C”, the left surround signal “SL”, the right surroundsignal “SR”, and the low frequency effect signal “LFE”. The losslessdecoder 3F decodes the first information into the addition-result signal(L+R) and the subtraction-result signal (L−R) as the lossless decoder 3Din FIG. 1 does. The lossless decoder 3F outputs the addition-resultsignal (L+R) and the subtraction-result signal (L−R) to the channelcorrelation circuit “B”. Similarly, the lossless decoder 3F decodes thesecond information into the center signal “C”, the left surround signal“SL”, the right surround signal “SR”, and the low frequency effectsignal “LFE”. The lossless decoder 3F outputs the center signal “C”, theleft surround signal “SL”, the right surround signal “SR”, and the lowfrequency effect signal “LFE”.

Eighth Embodiment

[0127]FIG. 19 shows an eighth embodiment of this invention which issimilar to the first embodiment thereof except for design changesindicated hereinafter.

[0128] The embodiment of FIG. 19 includes channel correlation circuitsA3 and B3 which replace the channel correlation circuits “A” and “B”(see FIG. 1) respectively, The channel correlation circuit A3 includes a½ divider 5 a 3 connected between an addition circuit 1 a and a losslessencoder 2D. Also, the channel correlation circuit A3 includes a ½divider 5 b 3 connected between a subtraction circuit 1 b and thelossless encoder 2D. The ½ dividers 5 a and 5 b (see FIG. 1) are removedfrom the channel correlation circuit B3.

Ninth Embodiment

[0129]FIG. 20 shows a ninth embodiment of this invention which issimilar to the seventh embodiment thereof except for design changesindicated hereinafter.

[0130] The embodiment of FIG. 20 includes channel correlation circuitsA3 and B3 which replace the channel correlation circuits “A” and “B”(see FIG. 17) respectively. The channel correlation circuit A3 includesa ½ divider 5 a 3 connected between an addition circuit 1 a and alossless encoder 2F. Also, the channel correlation circuit A3 includes a½ divider 5 b 3 connected between a subtraction circuit 1 b and thelossless encoder 2F. On the other hand, ½ dividers 5 a and 5 b (see FIG.17) are removed from the channel correlation circuit B3.

What is claimed is:
 1. An audio signal encoding apparatus comprising:means for adding a first audio signal and a second audio signal into anaddition-result signal; means for subtracting the first audio signalfrom the second audio signal, and generating a subtraction-resultsignal; means responsive to the addition-result signal for generating afirst difference signal representing a difference in the addition-resultsignal; means responsive to the subtraction-result signal for generatinga second difference signal representing a difference in thesubtraction-result signal; a plurality of first predictors havingdifferent prediction characteristics respectively and being responsiveto the first difference signal for generating first different predictionsignals for the first difference signal, respectively; a plurality offirst subtracters for generating first prediction-error signalsrepresenting differences between the first difference signal and thefirst different prediction signals, respectively; means for selecting afirst minimum prediction-error signal representative of a smallestdifference from among the first prediction-error signals; a plurality ofsecond predictors having different prediction characteristicsrespectively and being responsive to the second difference signal forgenerating second different prediction signals for the second differencesignal, respectively; a plurality of second subtracters for generatingsecond prediction-error signals representing differences between thesecond difference signal and the second different prediction signals,respectively; and means for selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals.
 2. An audio signal encoding apparatus asrecited in claim 1, further comprising means for generating avariable-rate bit stream in response to the first minimumprediction-error signal and the second minimum prediction-error signal.3. An audio signal decoding apparatus for processing a first minimumprediction-error signal and a second minimum prediction-error signalwhich are generated by an audio signal encoding apparatus comprisingmeans for adding a first audio signal and a second audio signal into anaddition-result signal; means for subtracting the first audio signalfrom the second audio signal, and generating a subtraction-resultsignal; means responsive to the addition-result signal for generating afirst difference signal representing a difference in the addition-resultsignal; means responsive to the subtraction-result signal for generatinga second difference signal representing a difference in thesubtraction-result signal; a plurality of first predictors havingdifferent prediction characteristics respectively and being responsiveto the first difference signal for generating first different predictionsignals for the first difference signal, respectively; a plurality offirst subtracters for generating first prediction-error signalsrepresenting differences between the first difference signal and thefirst different prediction signals, respectively; means for selecting afirst minimum prediction-error signal representative of a smallestdifference from among the first prediction-error signals; a plurality ofsecond predictors having different prediction characteristicsrespectively and being responsive to the second difference signal forgenerating second different prediction signals for the second differencesignal, respectively; a plurality of second subtracters for generatingsecond prediction-error signals representing differences between thesecond difference signal and the second different prediction signals,respectively; and means for selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals; the audio signal decoding apparatuscomprising: means for recovering the addition-result signal from thefirst minimum prediction-error signal; means for recovering thesubtraction-result signal from the second minimum prediction-errorsignal; and means for recovering the first audio signal and the secondaudio signal from the recovered addition-result signal and the recoveredsubtraction-result signal.
 4. A method comprising the steps of. adding afirst audio signal and a second audio signal into an addition-resultsignal; subtracting the first audio signal from the second audio signal,and generating a subtraction-result signal; generating a firstdifference signal representing a difference in the addition-resultsignal; generating a second difference signal representing a differencein the subtraction-result signal; generating first different predictionsignals for the first difference signal, respectively; generating firstprediction-error signals representing differences between the firstdifference signal and the first different prediction signals,respectively; selecting a first minimum prediction-error signalrepresentative of a smallest difference from among the firstprediction-error signals; generating second different prediction signalsfor the second difference signal, respectively; generating secondprediction-error signals representing differences between the seconddifference signal and the second different prediction signals,respectively; selecting a second minimum prediction-error signalrepresentative of a smallest difference from among the secondprediction-error signals; and transmitting the first minimumprediction-error signal and the second minimum prediction-error signalto a communication line.
 5. An optical recording medium storingformatted information of a first minimum prediction-error signal and asecond minimum prediction-error signal which are generated by an audiosignal encoding apparatus comprising means for adding a first audiosignal and a second audio signal into an addition-result signal; meansfor subtracting the first audio signal from the second audio signal, andgenerating a subtraction-result signal; means responsive to theaddition-result signal for generating a first difference signalrepresenting a difference in the addition-result signal; meansresponsive to the subtraction-result signal for generating a seconddifference signal representing a difference in the subtraction-resultsignal; a plurality of first predictors having different predictioncharacteristics respectively and being responsive to the firstdifference signal for generating first different prediction signals forthe first difference signal, respectively; a plurality of firstsubtracters for generating first prediction-error signals representingdifferences between the first difference signal and the first differentprediction signals, respectively; means for selecting a first minimumprediction-error signal representative of a smallest difference fromamong the first prediction-error signals; a plurality of secondpredictors having different prediction characteristics respectively andbeing responsive to the second difference signal for generating seconddifferent prediction signals for the second difference signal,respectively; a plurality of second subtracters for generating secondprediction-error signals representing differences between the seconddifference signal and the second different prediction signals,respectively; and means for selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals.
 6. A method of network-based transmission,comprising the steps of: adding a first audio signal and a second audiosignal into an addition-result signal; subtracting the first audiosignal from the second audio signal, and generating a subtraction-resultsignal; generating a first difference signal representing a differencein the addition-result signal; p1 generating a second difference signalrepresenting a difference in the subtraction-result signal; generatingfirst different prediction signals for the first difference signal,respectively; generating first prediction-error signals representingdifferences between the first difference signal and the first differentprediction signals, respectively; selecting a first minimumprediction-error signal representative of a smallest difference fromamong the first prediction-error signals; generating second differentprediction signals for the second difference signal, respectively;generating second prediction-error signals representing differencesbetween the second difference signal and the second different predictionsignals, respectively; selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals; and transmitting the first minimumprediction-error signal and the second minimum prediction-error signalto a communication line.
 7. An audio signal encoding apparatuscomprising: means for selecting a first audio signal and a second audiosignal from among signals composing a multi-channel audio signal; meansfor adding the first audio signal and the second audio signal into anaddition-result signal; means for subtracting the first audio signalfrom the second audio signal, and generating a subtraction-resultsignal; means responsive to the addition-result signal for generating afirst difference signal representing a difference in the addition-resultsignal; means responsive to the subtraction-result signal for generatinga second difference signal representing a difference in thesubtraction-result signal; a plurality of first predictors havingdifferent prediction characteristics respectively and being responsiveto the first difference signal for generating first different predictionsignals for the first difference signal, respectively; a plurality offirst subtracters for generating first prediction-error signalsrepresenting differences between the first difference signal and thefirst different prediction signals, respectively; means for selecting afirst minimum prediction-error signal representative of a smallestdifference from among the first prediction-error signals; a plurality ofsecond predictors having different prediction characteristicsrespectively and being responsive to the second difference signal forgenerating second different prediction signals for the second differencesignal, respectively; a plurality of second subtracters for generatingsecond prediction-error signals representing differences between thesecond difference signal and the second different prediction signals,respectively; and means for selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals.
 8. An audio signal encoding apparatus asrecited in claim 7, further comprising means for generating avariable-rate bit stream in response to the first minimumprediction-error signal and the second minimum prediction-error signal.9. An audio signal decoding apparatus for processing a first minimumprediction-error signal and a second minimum prediction-error signalwhich are generated by an audio signal encoding apparatus comprisingmeans for selecting a first audio signal and a second audio signal fromamong signals composing a multi-channel audio signal; means for addingthe first audio signal and the second audio signal into anaddition-result signal; means for subtracting the first audio signalfrom the second audio signal, and generating a subtraction-resultsignal; means responsive to the addition-result signal for generating afirst difference signal representing a difference in the addition-resultsignal; means responsive to the subtraction-result signal for generatinga second difference signal representing a difference in thesubtraction-result signal; a plurality of first predictors havingdifferent prediction characteristics respectively and being responsiveto the first difference signal for generating first different predictionsignals for the first difference signal, respectively; a plurality offirst subtracters for generating first prediction-error signalsrepresenting differences between the first difference signal and thefirst different prediction signals, respectively; means for selecting afirst minimum prediction-error signal representative of a smallestdifference from among the first prediction-error signals; a plurality ofsecond predictors having different prediction characteristicsrespectively and being responsive to the second difference signal forgenerating second different prediction signals for the second differencesignal, respectively; a plurality of second subtracters for generatingsecond prediction-error signals representing differences between thesecond difference signal and the second different prediction signals,respectively; and means for selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals; the audio signal decoding apparatuscomprising: means for recovering the addition-result signal from thefirst minimum prediction-error signal; means for recovering thesubtraction-result signal from the second minimum prediction-errorsignal; and means for recovering the first audio signal and the secondaudio signal from the recovered addition-result signal and the recoveredsubtraction-result signal.
 10. A method comprising the steps of:selecting a first audio signal and a second audio signal from amongsignals composing a multi-channel audio signal; adding the first audiosignal and the second audio signal into an addition-result signal;subtracting the first audio signal from the second audio signal, andgenerating a subtraction-result signal; generating a first differencesignal representing a difference in the addition-result signal;generating a second difference signal representing a difference in thesubtraction-result signal; generating first different prediction signalsfor the first difference signal, respectively; generating firstprediction-error signals representing differences between the firstdifference signal and the first different prediction signals,respectively; selecting a first minimum prediction-error signalrepresentative of a smallest difference from among the firstprediction-error signals; generating second different prediction signalsfor the second difference signal, respectively; generating secondprediction-error signals representing differences between the seconddifference signal and the second different prediction signals,respectively; selecting a second minimum prediction-error signalrepresentative of a smallest difference from among the secondprediction-error signals; and transmitting the first minimumprediction-error signal and the second minimum prediction-error signalto a communication line.
 11. An optical recording medium storingformatted information of a first minimum prediction-error signal and asecond minimum prediction-error signal which are generated by an audiosignal encoding apparatus comprising means for selecting a first audiosignal and a second audio signal from among signals composing amulti-channel audio signal; means for adding the first audio signal andthe second audio signal into an addition-result signal; means forsubtracting the first audio signal from the second audio signal, andgenerating a subtraction-result signal; means responsive to theaddition-result signal for generating a first difference signalrepresenting a difference in the addition-result signal; meansresponsive to the subtraction-result signal for generating a seconddifference signal representing a difference in the subtraction-resultsignal; a plurality of first predictors having different predictioncharacteristics respectively and being responsive to the firstdifference signal for generating first different prediction signals forthe first difference signal, respectively; a plurality of firstsubtracters for generating first prediction-error signals representingdifferences between the first difference signal and the first differentprediction signals, respectively; means for selecting a first minimumprediction-error signal representative of a smallest difference fromamong the first prediction-error signals; a plurality of secondpredictors having different prediction characteristics respectively andbeing responsive to the second difference signal for generating seconddifferent prediction signals for the second difference signal,respectively; a plurality of second subtracters for generating secondprediction-error signals representing differences between the seconddifference signal and the second different prediction signals,respectively; and means for selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals.
 12. A method of network-based transmission,comprising the steps of: selecting a first audio signal and a secondaudio signal from among signals composing a multi-channel audio signal;adding the first audio signal and the second audio signal into anaddition-result signal; subtracting the first audio signal from thesecond audio signal, and generating a subtraction-result signal;generating a first difference signal representing a difference in theaddition-result signal; generating a second difference signalrepresenting a difference in the subtraction-result signal; generatingfirst different prediction signals for the first difference signal,respectively; generating first prediction-error signals representingdifferences between the first difference signal and the first differentprediction signals, respectively; selecting a first minimumprediction-error signal representative of a smallest difference fromamong the first prediction-error signals; generating second differentprediction signals for the second difference signal, respectively;generating second prediction-error signals representing differencesbetween the second difference signal and the second different predictionsignals, respectively; selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals; and transmitting the first minimumprediction-error signal and the second minimum prediction-error signalto a communication line.